Digestion in monogastric mammals

The small intestine, which comprises the duodenum, the jejunum and the ileum, is the main absorption site and contains a series of finger-like projections, the vilh, which greatly increase the surface area available for absorption of nutrients. Each villus contains an arteriole and venule, together with a drainage tube of the lymphatic system, a lacteal. The venules ultimately drain into the hepatic portal system, and the lacteals into the thoracic lymphatic duct. The luminal side of each villus is covered with projections, the microvilli, which are often referred to as the brush border. 

There are a number of secretions that flow into the alimentary canal from the liver, the pancreas and the wall of the canal, and many of these contain enzymes that bring about the hydrolysis of the various food components (see Table 8.1). Some of the proteolytic enzymes present in the secretions are initially in the form of inactive precursors termed zymogens. These are activated after secretion into the tract. 

Recommended name Trivial name Systematic name Number Source Substrate 

Chymosin Rennin - 3.4.23.4 Gastric mucosa (young calves) Proteins and peptides 

Carboxypeptidase A Carboxypeptidase Peptidyl-L-amino-acid hydrolase 3.4.12.2 Small intestine Peptides 

---